KT88s for Audio Research VS55

Is it possible to use KT88s for the AR VS55 amp? Has anyone done this - I hear that they are quite different than the 6550 tube. I just replaced the input tubes w/ Sovtek cryo tubes and the difference is stunning, to say the least.

I read somewhere (don't remember where) that apparently Audio Research does not approve the use of KT88s in their amps. If I were you I would call them and ask to be sure.

How do you like the VS55 vs the Krell?

I'd been using NOS Phillips ECG's in my Cary SLM-100's for a long time, and couldn't bare the thought of changing to new production anything. That was until I found out what the prices had done on matched octets of ANYTHING NOS. Almost impossible to find now anyway! I bought a matched octet of the latest Winged 'C' 6550's from Upscale, and was very presently surprised. They are actually more open than the Phillips. Now- IF someone could only create a 6SN7 that could even come close to the TungSol VT-231 round plate(driver) and Sylvania 6SN7W tallboys(phase splitter) I'm using........Well, I hope my hearing goes before they do! Maybe I should start playing the lottery.
I'm not sure if the VS55 can handle KT88's. A lot of ARC's can even though they don't support it. And, KT88's will definitely sound different (and different brands of KT88's sound different from each other as well) so it pays to think about what sound you are trying to make before you leap.

One of the principal reasons ARC wants folks to use SED6550's (OEM tube) is that they are rugged and rarely fail. (Many popular KT88's are not rugged, i.e. they are failure prone) This has been important because their biasing circuit is not fused and if a power tube shorts out it will take out a resistor in the bias circuit as well as the main fuse. The latter's no big deal, but unless you are handy you have to find a techie to install a new resistor. I had to send my amp back to ARC for repairs, a PITA.

Again, Im not familar with your amp. But I'd be inclined to follow thier advise. Besides, I like SED 6550's in several non-ARC amps I use as well as the ARC I used to use.

There is absolutely no comparison between the Krell and ARC - as they say "tubes rule"!!

Thanks everyone for your thoughts - Eventually I will probably try a better quality 6550, maybe cryo'd.

Regards, Jason.